• Journal of Surface Science and Engineering
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• v.57 no.5
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• pp.425-431
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• 2024

As demand in the electric vehicle market increases, the development of high capacity, high energy density lithium-ion batteries (LIBs) is required. Silicon has a extremely high theoretical capacity of 4200 mAh/g, but low cycle life and structural instability due to high volume expansion during charging and discharging are critical issue to solve. A reduced silicon oxide has also a high theoretical capacity of 2500 mAh/g and recently studied extensively for its low-cost, superior cycle life, and structural stability. In this study, we first synstheized SiO₂ particles by sol-gel method using tetraethyl orthosilicate (TEOS) precursor. The SiO₂ particle size was controlled with an average particle size of 300-600 nm by the addition amount of TEOS, NH₃, and H₂O. The synthesized SiO₂ particles were reduced to SiO_x through the magnesiothermic reduction reaction (MRR), and electrochemical characteristics were evaluated according to the particle size of SiO_x. For electrochemical characterization, SiO_x (10 wt.%) was mixed with graphite, and 2032 half cells were fabricated to obtain charge-discharge curve, cycle performance, rate performance, and electrochemical impedance spectroscopy curves. As a result, the mean size of SiO_x particle decreases from 600 to 300 nm, the initial discharge capacity increases from 459.9 to 556.5 mAh/g with the single capacity from 1359.4 to 2325.3 mAh/g, respectively. Finally, the present result shows the availability of MRR process to obtain reduced silicon oxide particles and sized dependent electrochemical properties to develop high capacity and high energy density LIBs.

• Applied Chemistry for Engineering
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• v.26 no.5
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• pp.543-548
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• 2015

Si/C/CNF composites as anode materials for lithium-ion batteries were examined to improve the capacity and cycle performance. Si/C/CNF composites were prepared by the fabrication process including the synthesis and magnesiothermic reduction of SBA-15 to obtain Si/MgO by ball milling and the carbonization of phenol resin with CNF and HCl etching. Prepared Si/C/CNF composites were then analysed by BET, XRD, FE-SEM and TGA. Among SBA-15 samples synthesized at reaction temperatures between 50 and $70^{\circ}C$, the SBA-15 at $60^{\circ}C$ showed the largest specific surface area. Also the electrochemical performances of Si/C/CNF composites as an anode electrode were investigated by constant current charge/discharge test, cyclic voltammetry and impedance tests in the electrolyte of LiPF6 dissolved in mixed organic solvents (EC : DMC : EMC = 1 : 1 : 1 vol%). The coin cell using Si/C/CNF composites (Si : CNF = 97 : 3 in weight) showed better capacity (1,947 mAh/g) than that of other composition coin cells. The capacity retention ratio decreased from 84% (Si : CNF = 97 : 3 in weight) to 77% (Si : CNF = 89 : 11 in weight). It was found that the Si/C/CNF composite electrode shows an improved cycling performance and electric conductivity.